Brake and Clutch Emissions Generated During Vehicle Operation

Our plain-English summary of Brake and Clutch Emissions Generated During Vehicle Operation, by M.G. Jacko, R.T. DuCharme, J.H. Somers (1973).

The study

• Authors: M.G. Jacko, R.T. DuCharme, J.H. Somers
• Published: Society of Automotive Engineers, Automotive Engineer Meeting. Detroit, Michigan. May 14-18, 1973.
• Type of article: Conference paper
• Our copy: from Johns-Manville's own medical library. The article is still under copyright, so we describe it here rather than post it.

In plain English

This 1973 engineering paper measured asbestos in wear debris from the brakes and clutch of one medium-weight passenger car. The friction materials contained chrysotile asbestos. The authors built sealed collectors for a front disc brake, a rear drum brake and the clutch. They ran three vehicle tests, about 8100 miles of mostly Detroit traffic driving plus harder fade tests, and examined the debris by microscopy. Asbestos made up on average 0.23% of the brake debris across the three tests, and 0.07% in the third test. Asbestos emissions were higher for new friction surfaces and decreased with use. Using national vehicle and friction-material data, the authors estimated a total asbestos emission of 158,200 lb a year for all US vehicles. Of this, they estimated 135,470 lb would drop onto the road, 17,670 lb would be retained in the brakes, and 5060 lb, or 3.2%, would go into the air. They also estimated that more than 99.7% of the asbestos is converted. The authors considered these estimates maximum values and said that, because of data uncertainties, emissions could only be considered a broad range.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Vehicle test study measuring brake and clutch wear debris with specially built emissions collectors, followed by a calculated estimate of asbestos emissions for all US vehicles
• Who was studied: One medium-weight passenger car (4850 lb test weight) with front disc brakes, rear drum brakes, a three-speed manual transmission and a dry clutch. It was driven about 8100 miles in three vehicle tests, about 90% of them in Detroit traffic, using original-equipment and aftermarket friction materials from five manufacturers. The national estimate was based on US motor vehicle population data.
• Exposure: Asbestos (chrysotile) in automotive friction materials (disc pads, drum brake linings, clutch facings), worn during low-temperature driving (Detroit Traffic Test) and high-temperature fade tests
• Main results:
  • Across all three vehicle tests, the overall average asbestos content of the brake emissions was 0.23%
  • In vehicle test 2 the overall average asbestos content of brake emissions was 0.25%; in vehicle test 3 it was 0.07%
  • An independent check by Battelle Columbus Laboratories on 24 samples gave lower values: the Program average was 0.24% and the Battelle average was 0.17%, or 69% of the Program average
  • For both disc and drum brakes, the surfaces sample was the largest of the three debris fractions (~92%), followed by the sump sample (~7%) and the airborne sample (~1%)
  • Asbestos emissions were higher for new friction surfaces and decreased with use
  • The estimated total asbestos emission for the test car was 28.51 micrograms per mile
  • The estimated asbestos emission for US passenger cars (96.4 million vehicles) was 60,400 lb per year
  • For all US vehicles, the estimated total asbestos emission of 158,200 lb per year (Table 25) was split as follows: 135,470 lb (85.6%) road dropout, 17,670 lb (11.2%) retained in the brakes, and 5,060 lb (3.2%) airborne. The largest part was dropout material.
  • For all US vehicles, the estimated contribution to the atmosphere was 5060 lb, or 3.2% of the total asbestos emission
  • On average, more than 99.7% of the asbestos was estimated to be converted
• The authors' conclusion: The authors considered their estimates to be maximum values. They concluded that their total asbestos emission estimates, and especially the airborne estimate, were considerably lower than the 540,000 lb estimated by IIT Research Institute.
• Limitations the authors state:
  • Because of uncertainties in all of the data available, emissions could only be considered as a broad range rather than a single value
  • The estimate of driving in mountainous areas (11.5%) was largely subjective and may be high
  • The Program's asbestos figures were expected to run high because larger fiber bundles were assumed to be cylinders and all fibers were assumed to be 100% asbestos
  • Measurement error increased as the percentage of asbestos in a sample decreased
  • Truck and bus results were arbitrarily weighted from the passenger car test data

Topics

Medical terms in this study, explained in our Lexicon: Chrysotile.

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